Intracellular activation of complement C3 modulates tumor-associated macrophages polarization

Mounting evidence has highlighted the importance of complement in the construction of an immunosuppressive tumor microenvironment (TME). Tumor cell-derived C3 has been previously reported, however, whether and how it acts on anti-tumor immunity remains to be elucidated. Here, we describe a unique role of tumor cell-derived C3 in suppressing anti-tumor immunity. Tumor cell-derived C3 was activated intracellularly, which results in generation of C3a. C3a could modulate tumor-associated macrophages (TAMs) via C3a-C3aR-PI3Kγ signaling, thereby repressing anti-tumor immunity. More importantly, deletion of C3 in tumor cells with high C3 expression is sufficient to enhance the efficacy of ɑPD-L1 treatment. Collectively, our present results suggest tumor cell derived C3 may serve as a novel target in cancer immunotherapy, specifically targeting C3 in tumor cells to enhance anti-tumor immunity.